The invention relates to a method of providing a copper metallization on a dielectric or semiconductive body. The invention also relates to a method of providing a copper metallization on a base metal electrode multilayer capacitor. The invention further relates to a metallized dielectric or semiconductive body.
Dielectric and semiconductive materials have many uses, particularly as electronic components. For example, dielectric ceramics having a perovskite structure make very good capacitors. Barium titanate and calcium zirconate ceramics are typically used for such purposes. Other oxides may also be used.
In electronic components made of dielectric or semiconductive materials, electrical connections to the components must be provided. These are typically provided in the form of metal electrodes, or metallizations, which are attached to the component body. Noble metals such as silver and palladium and alloys thereof make excellent electrodes due to their excellent electrical conductivities and due to their resistance to chemical oxidation. However, such electrodes are very expensive.
Alternatively, less expensive base metals may be used for metallizations on components. For example, conductive films made partially of nickel, cobalt, and copper have been made in the past. (See, e.g. U.S. Pat. No. 4,122,232.) Some of the considerations affecting the use of such base metal metallizations include their susceptibility to oxidation and the strength of the bond attaching the metallization to the dielectric. In the case of copper metallizations, additional problems include the difficulty and expense of obtaining an easily dispersible copper powder (that is, the difficulty and expense of attaching a molecule to the copper particle which will interact properly with the solvent system), and the maleability of the copper which makes it difficult to grind the copper into a powder form while controlling particle size, agglomeration and surface area.
A particularly novel approach which reduces some of the problems associated with the formation of copper metallizations is disclosed in U.S. Pat. No. 2,993,815 (Treptow). Treptow discloses a method of providing a copper metallization on a refractory substrate. First, a mixture of copper or copper oxide and reduction-resistant glass frit is suspended in a volatile medium to form a dispersion. This mixture is applied to a substrate, and the coated substrate is then fired in an oxidizing atmosphere to form a bond between the substrate, glass, and copper oxide. After oxidation, the coated substrate is fired in an atmosphere reducing to the copper oxide, so as to reduce the copper oxide to copper metal.
While the method disclosed by Treptow for producing copper metallizations is effective, it is a process requiring many steps. Moreover, the glass frit appears to create strains at the metallization-substrate interface due to (i) the creation of reaction zones where the glass frit tends to react with the ceramic body, and (ii) a mismatch between the thermal coefficients of the glass, the glass-substrate reaction zone, and the substrate. (See, e.g. "Non-Noble Termination Method for Chip Capacitors," R. H. Marion et al., The International Journal For Hybrid Microelectronics, Vol. 5, No. 2, 1982, pp. 50-53.) These strains sometimes result in cracks in the dielectric upon thermal cycling. Additionally, the glass frit is vulnerable to chemical attack which may occur during subsequent processing of the component. For example, if the metallized component is electroplated to provide a solderable terminal, the electroplating may chemically attack the glass frit in the metallization.